Oral sodium phosphate (NaP), a small volume hypertonic solution of sodium phosphate salts, has emerged as a favorable alternative to large volume polyethylene glycol (PEG)-electrolyte solutions for rapid colonic cleansing prior to colonoscopy. Randomized controlled trials1-4 have demonstrated equivalent efficacy and superior tolerability of NaP compared to PEG-electrolyte formulations. Consequently, it has become widely used and increasingly is considered the agent of choice for colonic purgation.5 
With the growing demand for colonoscopy, the importance of optimizing the safety of this procedure becomes increasingly relevant. Although NaP is safe in most patients, its osmotic action has raised concerns about intravascular volume contraction.7 Previous studies in which hemodynamic variables were measured during oral NaP-based colonic preparation showed evidence of plasma hypovolemia in between 7 to 30% of patients.1,7 The recent report in a young healthy patient of severe NaP-induced hyperphosphatemia, hypocalcemia and hypomagnesemia,17 attributed primarily to inadequate fluid consumption, underscores the importance of optimizing plasma volume status during NaP treatment.